The effects of root-zone temperature (RZT) on P and Zn interactions in 14- and 20-d-old barley (Hordeum vulgare L., cv. Herta) were studied in a nutrient solution experiment. The treatments consisted of two RZTs (10 and 20°C), three levels of Zn (0, 0.5, and 5.0 µM), and two levels of P (200 and 2000 µM) in a factorial arrangement. Highly significant interactions were found involving RZT, Zn and P, demonstrating the dependence of the P-Zn interaction on RZT. A marked effect of increased Zn supply on decreasing the P concentrations in plant tops and oldest leaves was greatest for plants grown at a RZT of 20°C and supplied high P. For 20-d-old plants grown at 10°C RZT, increasing the P supply had no significant effect on the P concentrations in the shoots, although increasing the Zn supply depressed the P concentrations. The RZT significantly affected the calculated uptake rates of mineral elements. Surprisingly, mean uptake rates of Ca, Mn, Cu, Fe, and Zn were the same or higher at 10°C as at 20°C RZT. Roots grown at the colder RZT contained much higher concentrations of Zn, Fe, and Cu; they were also higher in Mg and S but lower in P and K. Gross root morphology was affected by RZT. The colder RZT resulted in plants with shorter, thicker roots, and fewer secondary roots. This low RZT effect was not influenced by Zn or P treatment and could not be attributed solely to slower root growth rates at the lower RZT.